..thanks,upsidedown
i was not considering this even worst case
If you are going to transfer some information (such as a device ID)
across your link, you need to consider also blocking issues with such
simple receivers.
We have a club building on top of a hill with a 434 MHz 30 W repeater
on the roof. We had problems with illegally parked cars outside the
building. One way to scare these cars away was to look when the car
owner approached his car, was to fire up the transmitter and the car
owner tried frantically to open the car doors with his key transmitter
at 433.92 MHz. The receiver in the car had so bad selectivity, that it
was completely blocked by the strong signal nearly 1 MHz away.
If you are going to use some simple LC front head for RF detection,
you need much more selectivity for any actual data extraction to
reliably work in the RF polluted world.
I would suggest using a proper receiver with passive LC front end and
proper IF filtering or zero-IF (I/Q) system which is activated for
very short periods of time. Here is the critical issue, how fast will
the local oscillator start. Some PLL constructs are notoriously (1 s)
slow to stabilize, forcing to use very long activation periods and
hence large average consumption.
However, if the crystal oscillator and some DDS construct starts in
less than 1 ms, you should be able to power up the receiver for 1 ms
every 1 s, the duty cycle is 1:1000, compensating for the high current
consumption of a decent receiver. You may have to take the RF-sense
after some 16 kHz FM filters, if you are going to use only 1 ms
sampling periods, even if you use 100Hz final filters for data
extraction when the RF appears to be strong and hence constantly turn
on the receiver.
